Then there's Kravis' business partner and cofounder of Kohlberg Kravis Roberts (KKR), George Roberts. Roberts and Kravis are also cousins. But while Roberts is worth just as much as Kravis—$5.2 billion at last count—he's not been in the spotlight as much as his cousin.

This is definitely a guy worth paying attention to—not just because of the size of his fortune, but because he's an experienced and sophisticated philanthropist. And while the annual giving numbers aren't yet huge, that's likely to change at some point, as it often does when titans of business start thinking more about their legacy. (Roberts is 71.)

George Roberts has a couple of key interests in philanthropy that are important to know about.

1. He Was a Pioneering Funder of Social Enterprises

Roberts is one of a growing list of business types applying the skills they use in business to philanthropy. The difference here is that Roberts has been doing this for 20 years, and is something of a pioneer in this area. While Roberts and his first wife founded a traditional charitable foundation in the 1980s called the Roberts Foundation—which I'll get back to in a minute—in the 1990s, he started looking at market-based ways to tackle issues of poverty, job creation, and homelessness in the San Francisco Bay Area and beyond. One of Roberts' first forays was called the Homeless Economic Development Fund, which supported employment-related nonprofits during the early and mid-1990s.

Later, in 1997, this turned into the Roberts Economic Development Fund, which is now just known as REDF. According to its website, REDF has "supported 50 social enterprises that employ 9,000 people, generating more than $140 million in revenues." Some of their partners include the Community Housing Partership in San Francisco, and Goodwill of Silicon Valley. Roberts pumps some of his own money into REDF through the Roberts Foundation.

2. Roberts Loves His Alma Maters

Roberts is another billionaire philanthropist who gives love to the schools that shaped him. What's notable here, though, is that it's not places like Harvard or Yale that are getting his money. Roberts attended a small liberal arts college outside of Los Angeles called Claremont McKenna, to which he gave $50 million alone in 2012. Buildings, scholarships and even the Roberts Pledge are staples on the campus. At a place like Claremont McKenna, Roberts money definitely goes a long way, and he's been a longtime supporter.

What's more, prior to attending Claremont McKenna, Roberts went to Culver Military Academy, which is part of a consortium of schools called Culver Academies in Indiana. Again, Culver is not the kind of place that's in the spotlight, but Roberts has supported the school with millions over the years. Finally, Roberts has given modest sums to UC Hastings College of Law, where he got his J.D.

3. The Bay Area is the Major Focus of Roberts' Philanthropy

Through the Roberts Foundation, Roberts and his wife Linnea make many of their grants to Bay Area outfits. Roberts' wife sits on the board at San Francisco Museum of Modern Art, which has received modest sums recently. SF Ballet received $5 million in 2012, while San Francisco Symphony, and San Francisco Opera have also seen support. In health, recent sums have gone to the UCSF Cancer Center, which received at least $1 million in 2013.

Roberts money also finds its way to animal and environmental causes, and this may be in part because of Roberts' first wife, Leanne, who was a prominent board member of the San Francisco SPCA. In 2009, the SF SPCA opened the Leanne B. Roberts Animal Care Center. These days, Roberts' son, Eric, who's on the board at the Roberts Foundation, sits in the board seat once occupied by Leanne at the SF SPCA. A little under $500,000 recently went to the Ark Watch Foundation in Northern California, whose mission is to "improve the welfare of animals in need within the U.S. and Canada." Another $700,000 also recently went to Del Monte Forest Conservancy in Pebble Beach "which conserves, acquires and enhances lands dedicated to open space within Del Monte Forest."